linux-kernel - question about smatch error

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Message-ID: <adar5ccyver.fsf@cisco.com>
Date:	Sun, 16 Jan 2011 21:02:52 -0800
From:	Roland Dreier <rdreier@...co.com>
To:	Dan Carpenter <error27@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: question about smatch error

Hi Dan,

I'm running smatch against some of my code, and I'm seeing the errors

drivers/infiniband/hw/mlx4/main.c +784 mlx4_addrconf_ifid_eui48(5) error: buffer overflow 'eui' 3 <= 3
drivers/infiniband/hw/mlx4/main.c +785 mlx4_addrconf_ifid_eui48(6) error: buffer overflow 'eui' 3 <= 4
drivers/infiniband/hw/mlx4/main.c +787 mlx4_addrconf_ifid_eui48(8) error: buffer overflow 'eui' 3 <= 3
drivers/infiniband/hw/mlx4/main.c +788 mlx4_addrconf_ifid_eui48(9) error: buffer overflow 'eui' 3 <= 4

and I can't understand what smatch is trying to say -- the code in
question is basically

	if (vlan_id < 0x1000) {
		eui[3] = vlan_id >> 8;
		eui[4] = vlan_id & 0xff;
	} else {
		eui[3] = 0xff;
		eui[4] = 0xfe;
	}

where eui is a u8*, and I don't see how smatch even thinks it knows how
big the buffer is in the first place.

This is with up-to-date smatch from git (my tree is at 798c4c13).

Thanks,
  Roland
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